Gun propellant



States Bdlbddb Patented Dec. 31, 1863 Filed Mar. 25, 195d, Ser. No. 891,971 3 filaims. (fCl. 1 59- 168) ranted under 3S, Code (3952}, sec. 256) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the paymen of any royalties thereon or therefor.

T his invention relates generally to the field of ordnance and is more particularly concerned with an improved gun propellant composition.

It has been known for some time that wear i.e. erosion of the interior of the gun barrel is caused by three things: high temperature of the gases formed upon ignition of the gun propellant, the corrosive eflfect of these gases upon the metal of the barrel, and mechanical wear as the proiectile moves through the barrel. The latter cause is more or less unavoidable. In the past, attempts have been made to produce a satisfactor gun powder or propellant which minim'zes gun Wear due to the temperature and corrosivity or" the combustion gases. Some better known propellants of this type are Cordite N and Cool Picrite both of w ich consist chiefly of nitroglycerin, nitrocellulose, nitroguanidine with ethyl centralite as a coolant alons with a small percentage of volatiles. The ignition of these compositions produces gases which are rich in ammonia and cause discomfort to the gun crew. F rthermore, nitroguani ine is not produced in quantity in this country and therefore might not be in adequate supply during time of need.

Other formulations have been compounded with a View toward reducing the flame temperature of the gas produced upon ignition of the propellant. For example U.S. Patent No. 1,651,459 to Keck describes a gunpowder containing a large percentage of nitrocellulose and a small percentage of nitrated vegetable oil. As stated by Keck, the temperature of the gases discharged from the muzzle of the gun, is below that required for further combustion. Keck states that this reduces flash. By that he proba ly meant secondary flash caused by reignition of the gases in the oxygen of the atmosphere. Primary flash would, of course, be present in the Keel; composition. The prior art cool compositions are suitable for use in guns which are fired slowly, however, t..ey tend to erode the gun barrel when the gun is fired rapidly. The Keck composition also produces great quantities of carbon deposits resulting from the high ratio of carbon to hydrogen and oxygen in the for nulation. The effect of the carbon deposits is cumulative and quickly causes th breech mechanism to seize and bind after a burst is tired, thereby rendering the gun inoperative.

it is therefore one object of this invention to provide a new and improved gun propellant composition which has a relatively low adiabatic flame temperature and reduces erosion of the gun barrel.

Another object is the provision of an improved gun propellant composition having a low adiabatic flame temperature and does not produce any carbon deposits upon ignition so that it is suitable for prolonged use in rapid fire guns.

Still another object is the provision of a new and improved gun propellant which does not contain any critical materials.

These and many other objects will become more readily apparent when the following specification is understood.

Propellants manufactured in accordance with this invention may contain a large percentage of about twelve percent nitration nitrocellulose. The propellants optionally may contain a few percent of an inorganic salt such as potassium sulfate, potassium nitrate, or cryolite used as a primary flash suppressant in accordance with conventional practice. In the event that the propellant is to be used for night firing, it is preferable that the flash suppressant be added. The propellant may also contain a coolant such as symmetrical-diethyldiphenylurea (centralite) or butyl stearate. A stabilizer such as centralite may be added. Furthermore, the propellant may contain a small quantity of basic lead carbonate which has a relatively low decomposition temperature and upon ignition of the propellant decomposes to form molten lead. This molten lead serves as a gun bore lubricant. Varying amounts of volatiles are employed as a processing additive. As used in this specification volatiles may be defined to mean such things as water, alcohol and ether.

The process for preparing the instant gun propellant follows standard procedures for propellant manufacture. The nitrocellulose is mixed with alcohol and ether to form a colloidal mixture.

The nitrocellulose may be colloided by the conventional method of forcing the alcohol and other into the fibers to form a solid colloid. The material is broken up mechanically and the proper amounts of the other constituents are added to give the desired ratio of nitrocellulose to coolant, stabilizer and flash suppressant (if any}. As is usually done, an excess amount of volatiles is added. The mix is then placed in a drying room and maintained at a slightly elevated temperature to vaporize the excess volatiles. Periodically, a sample is withdrawn from the mix and its rate of burning is measured. As the percentage of volatiles decreases, the propellant becomes more quick, that is the linear burning rate is increased. This quicl'ness may be correlated to the ballistic properties of the propellant so that these properties may be controlled by providing the appropriate degree of quickness.

The composition of the propellants may be varied to provide a nominal adiabatic flame temperature Within the range K. to 2200 K. by adjusting the relative proportions of coolant and nitrocellulose. Within this range the propellants all exhibit suitable ballistic properties. Of course propellants having higher adiabatic flame temperatures also possess good ballistic prop rties. However, the higher the flame temperature, the greater is the gun erosion rate. For that reason, this invention is concerned only with those propellants in the aforementioned flame temperature range since they do not erode the gun barrel as rapidly as conventional gun propellants having higher adiabatic flame temperatures.

The propellant may contain from about two and one half percent by weight of coolant to about seven percent. The percent by weight of nitrocellulose in propellants embodying the principles of this invention may vary from about eighty-seven to ninety-two. The nitration is preferably about twelve percent which is lower than that used in Cordite hi or Cool licrite. The basic lead carbonate in the composition usually forms about one percent of the total weight of the propellant. The remainder of the composition may be volatiles or volatiles plus up to about three percent flash supressant.

The following examples are given by way of illustration and are not to be construed as limiting the invention in any way.

Example I Wt. percent Nitrocellulose 89 Centralite 6 Basic lead carbonate 1 Potassium sulfate Total volatiles 4 100 Example 2 Nitrocellulose 91.4

Centralite 3.8 Basic lead carbonate 1 Potassium sulfate Total volatiles 3.8

The calculated adiabatic flame temperatures of Examples 1 and 2 are 2000 K. and 2100 K. respectively.

The propellant compositions of Examples 1 and 2 were manufactured in prototype lots (50,000-1Q0,000 pounds) according to the aforementioned conventional process. Each of the propellants were used in 3" shells and were evaluated by extensive gun firing tests. The internal pressure within the gun was measured and found not to be excessive, the muzzle velocity and range were also found to be good for Examples 1 and 2 and for all the compositions of Examples 3-5, each of which were tested in a similar manner.

Further tests were conducted by firing shells from 3/50 gins at a rapid rate (90 rounds per minute). Several thousand rounds were fired from each gun while employing the propellant being tested. These tests duplicate tactical conditions of severe use for modern guns. There was no carbon fouling of the breach and each gun fired several thousand rounds Without seizing or binding. Many of the other gun propellants produce such large amounts of carbon that the breach locked after the first short burst. When a thousand rounds has been fired, the interior of the barrel was measured with a star gage to determine the amount of wear. Compared with similar tests of barrel erosion caused by conventional non hygroscopic propellants used during rapid fire, it was found that erosion was decreased by a factor of eight. It should be borne in mind that the non hygroscopic propellants are satisfactory when used during slow fire of these guns because the gun bore has a chance to cool slightly after each round is fired. Of course, rapid fire guns must be used in present day anti-aircraft systems so that a propellant useful only for slow fire is really of very slight value.

Example 3 Wt. percent Nitrocellulose 87.5 Centralite 6 Basic lead carbonate 1 Potassium sulfate 2 Total volatiles 3.5

100 Example 4 Nitrocellulose 89.4 Centralite 2.8 Basic lead carbonate 1 Poatssium sulfate 3 Total volatiles 3.8

The calulated adiabatic flame temperature of the flashless powder of Example 3 was 1950 K. and that of Example 4 was 2200 K. Firing tests in a 3"/70 gun following the procedure employed in Examples 1 and 2 showed that the erosion was only one half that of Cool Picrite propellant which up to now has been the best available Examples 5 a per- 0, porc, perd, percent cent cent cent Nitrocellulose Q0. 6 89. 2 91. 7 S9. 3 5 9 5.3 3. 3 2. 7 Ethyl Ccntralitc 1 l 1 1 Basic Lend Carbonate" 1 1 1 1 Potassium Sulfate 2 3 Total Volatiles 1. 5 1. 5 3 3 Examples 5a and 5c were tested in a 3"/50 gun following the same procedure as the testing of Examples 14. The results obtained were the same as in Examples 1 and 2. Examples 5!; and 5d performed about the same as Examples 3 and 4 when they were tested in a 3"/ 70 gun. The nitration of the nitrocellulose in all of the above examples was twelve percent.

The ballistic characteristics of all the propellants tested were found to be satisfactory. There was not any perceptible dirlerence between the ballistic performance of the propellants containing centralite and those containing butyl stearate as a coolant. However, the butyl stearatecontaining propellant is preferred because it has slightly better processing characteristics. It has been found to cure (lose volatiles) at a slightly greater rate and is easier to extrude into powder grains. Even those propellants containing butyl stearate as a coolant require small amounts of centralite as a stabilizer. Of course this added centralite also acts as an additional coolant.

it should be apparent to those skilled in the art that this invention provides a cool gun propellant which is especially suitable for use in a rapid fire gun. This invention may be practiced other than as set forth in the preceding illustrative examples. Accordingly, it is not to be construed as limited by these examples but within the scope of the following claims may be practiced other than as specifically set forth in these examples.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. A cool gun propellant consisting essentially of about 87% to 92% by weight of about 12% nitration nitrocellulose, 2 /2% to 7% by weight coolant selected from the group consisting of symmetrical die'thyl diphenyl urea and symmetrical diethyl diphenyl urea plus butyl stearate, about 1% by weight basic lead carbonate and up to about 3 cryolite, the remainder being water, alcohol and ether, s aid coolant being dispersed throughout the propellant.

2. A cool gun propellant consisting essentially of about 87% to 9 2% by weight of about 12% :of nitration nitrocellulose, 2 /2% to 7% by weight symmetrical diethyl diphenyl urea as coolant, about 1% by weight basic lead carbonate and up to about 3% by weight cryolite, the remainder being water, alcohol and ether, said coo lam being dispersed throughout the propellant.

3. A cool gun propellant consisting essentially of about 87% to 92% by weight of about 12% nitration nitrocellulose, 2 /2% to 6% by weight butyl stealrate as coolant, about 1% by weight symmetrical diethyl diphenyl urea, about 1% by weight basic llead carbonate and up to about 3% cryolite, the remainder being Water, alcohol and ether, said coolant being dispersed throughout the propellant.

(References on following page) 5 6 References Cited in the file of this patent 2,973,257 Ryker et a1. Feb. 28, 1961 UNITED STATES PATENTS 3,033,715 Preckel May 962 2,498,388 Ball Feb. 21, .1950 OTHER REFERENCES 2,701,524 Vane Dine Feb. 3, 1955 Kraus, Faube U. Lack 57, pp. 4337 (1951) (ab- 2,771,351 o m s et a N V- 1956 5 stracted in Chemical Abstracts), vol. 46, p. 1777; 1952. 

1. A COOL GUN PROPELLANT CONSISTING ESSENTIALLY OF ABOUT 87% TO 92% BY WEIGHT OF ABOUT 12% NITRATION NITROCELLULOSE, 2 1/2% TO 7% BY WEIGHT COOLANT SELECTED FROM THE GROUP CONSISTING OF SYMMETRICALDIETHYL DIPHENYL UREA AND SYMMETRICAL DIETHYL DIPHENY UREA PLUS BUTYL STEARATE, ABOUT 1% BY WEIGHT BASIC LEAD CARBONATE AND UP TO ABOUT 3% CRYOLITE, THE REMAINDER BEING WATER, ALCOHOL AND ETHER, SAID COOLANT BEING DISPERSED THROUGHOUT THE PROPELLANT. 